What is "too" low engine compressions?

[oldboyroy]

I have an O-360-A4M on my Cherokee and the engine is about 515 SMOH. My number three cylinder showed 63/80 on my annual. Yet the others are 70/80, 71/80, 73/80. Last year they were all lower 70s. Is this too low of a compression to fly safely? I fly the plane two to three times per month, the plane is not burning anymore than 1 quart every 10hrs. I have been using a new A&P for about four years (and very happy with him) - yet when I did, all my compressions were magically lower than the last A&P instruments. Could it be his instruments are a little off? Is it time to change a "jug"? My oil analysis looks regular...looking for advice?

 

[msires]

 

[N7655W]

 

[Ray93J]

 

[Highlnder]

 

[goldenflight]

 

[killrocks]

 

[dufur2003]

 

[flyguydon]

 

[PropFan]